1. Field of the Invention
The present invention relates to an electrical acoustic converter for generating a sound by vibrating a diaphragm by an electromagnet, more particularly, to a compact and thin-shaped electrical acoustic converter suitable for being mounted on a printed-circuit board or the like.
2. Description of the Prior Art
Recently, an electromagnetic sounder or electrical acoustic converter of a surface-mounted type, such as a miniature buzzer mounted directly on a printed-circuit board, becomes mainstream pursuant to increment of a surface-mounted technology of miniature electronic parts.
Therefore, a great number of electrical acoustic converters are used in a field of conductive-type speakers and multiple function-type speakers assembled in a mobile communication device such as a cellular phone.
A conventional electromagnetic sounder has coil contact springs provided outside an outer peripheral edge of a diaphragm for connecting an exciting coil with an outside power source, and the coil contact springs has terminals extending perpendicularly, as shown in Japanese Patent Laid Open 2001-306077, for example.
A typical example of a conventional electromagnetic-type sounder is illustrated in FIGS. 5 and 6. The electromagnetic-type sounder includes a case body 20 having a base cover 22 and a top cover 21 attached to the base cover 22. A sound-discharging hole 23 is provided between the top and base covers 21 and 22. A yoke 24 of a magnetic material is installed on a central portion of the base cover 22. The yoke 24 is provided at a center thereof with a center core 24a, and is formed at a portion of an outer periphery thereof with a cutout 24b, as shown in FIG. 5. An exciting coil 25 is disposed to surround the center core 24a. 
Disposed outside the exciting coil 25 is an annular magnet 26 having a cutout 26a provided to oppose the cutout 24b. A thin circular plate-shaped diaphragm 27 of a stainless material or the like is fixed on an upper surface of the base cover 22.
A circular plate-shaped exciting piece 28 of a magnetic material is fixed on a central portion of the diaphragm 27. A pair of lead frames 29 is embedded in the base cover 22 by insert mould. The lead frames 29 connect terminals 25a extending from a winding wire of the exciting coil 25 with outside connecting terminals (not shown).
One end of each lead frame 29 forms a terminal 29a being exposed from an upper surface of the base cover 22 at the cutout 24b of the yoke 24 and another end 29b of the lead frame 29 is disposed to be exposed within each of a pair of coil spring housings 22b formed outside the base cover 22.
The terminals 25a of the exciting coil 25 are electrically connected with the terminals 29a of the lead frames 29 by soldering or the like.
Coil contact springs 30 are inserted into the coil spring housings 22b to act as outside connecting terminals. A contact portion 30a of each of the coil contact springs 30 is electrically connected with the another end 29b of each lead frame 29 by soldering or the like, and a terminal 30b of each of the coil contact springs 30 is projected outwardly from the coil spring housing to connect with an outside part (not shown).
The coil spring housings 22b are formed outside an outside peripheral edge of the diaphragm 27.
In the electrical acoustic converter as described above, as a current is applied through coil contact springs 30 to the exciting coil 25 to excite it, a magnetic circuit passing the exciting coil 25, yoke 24, magnet 26 and exciting piece 28 is formed so that the exciting piece 28 is absorbed to the center core 24a to vibrate the diaphragm 27, thus making a sound. The generated sound is discharged passing through the sound-discharging hole 23 from a sound box formed by a space between the top cover 21 and diaphragm 27.
However, there is a problem in the above conventional acoustic converter that a compact and thinned electrical acoustic converter cannot be obtained because the coil contact springs are disposed outside the outer peripheral edge of the diaphragm, and furthermore because the terminals of the coil contact springs are extended perpendicularly.